1. Field of the Invention.
The present invention relates to hand held decimal timers for use in time studies of manufacturing processes.
2. Description of the related art including information disclosed under 37 CFR .sctn. 1.97-1.99.
Decimal timers, while similar to stop watches, differ in at least one very important way. A stop watch will typically measure time in the units of hours, minutes and seconds, where a minute is 1/60 of an hour and a second is 1/60 of a minute. Decimal timers come in more than one variety. Two of them being decimal minute timers and decimal hour timers. A decimal minute timer will measure time in only minutes with its fractional portion measured in decimal fractions of a minute. One quarter of a minute on a decimal minute counter will be represented as 0.25. On a stop watch the same quarter of a minute will be represented as 15 seconds. Decimal hour timers will measure time in only hours with its fractional portion measured in decimal fractions of an hour.
Several examples of previously proposed time study systems and timers are disclosed in the following U.S. Patents:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 3,657,488 Pountney et al. 4,168,525 Russell 4,413,277 Murray ______________________________________
Time studies of manufacturing processes are methods and tools for analyzing time efficiencies of a given manufacturing process and can be used to evaluate and target proposed changes and modifications in work procedures.
Decimal timers are of significant value in the area of time studies because times observed and recorded are often used in mathematical expressions to assist in the analysis of productivity of a worker. Whether it be for averaging times, for summing times to determine the total time required for a string of events, or any other form of mathematical analysis, the math associated with time studies is easier when the times are kept in decimal form.
FIG. 1 is a block diagram of a hand held decimal timer circuit 10 used in the prior art. The circuit includes a power supply 12, a counter circuit 14, a frequency divider circuit 16, a clock circuit 18, a display circuit 20 and a switch circuit 22.
The power supply 12 provides power to all the hand held decimal timer circuit elements referred to above.
The counter circuit 14 counts at the frequency provided by the frequency divider circuit 16 under the direction of control signals received from the switch circuit 22. It then sends the appropriate display signals to the display circuit 20.
The frequency divider circuit 16 converts a clock signal provided by the clock circuit 18 into a "count" signal at the frequency at which the counter circuit 14 should count.
The clock circuit 18 generates the clock signal for clocking the frequency divider circuit 16.
The display circuit 20 displays the count based on the display signals received from the counter circuit 14.
The switch circuit 22 provides an interface between the user and the counter circuit 14. It generates appropriate control signals for the counter circuit 14 based on the users input.
FIG. 2 illustrates a prior art frequency divider circuit 16 used in the Applicant's prior art hand held decimal timers. The frequency divider circuit 16 alternatively can be configured to function at the needed frequency for either a decimal hour timer or a decimal minute timer.
The frequency divider circuit 16 receives a 32.768 kHz clock signal 24 and this signal is used to clock a 12 bit binary counter 26. The 12 bit binary counter 26 is equivalent to a common digital logic component known in the electrical arts as a 4040. The 12 bit binary counter chip receives a positive supply voltage at pin 16 and is grounded at pin 8. The clock input for the chip, which receives the 32.768 kHz signal, is pin 10. A capacitor 28 is electrically connected to the reset input pin 11 of the 12 bit binary counter 26 to insure that the chip is properly reset on power up. The inputs to NAND gates 30 and 32 are electrically connected to Q3, Q4, Q5, Q8 and Q11 of the 12 bit binary counter 12, i.e., pins 6, 5, 3, 13 and 15 respectively. NAND gates 30 and 32 have their outputs electrically connected to the inputs of NOR gate 34 with the effect that when all the inputs for NAND gates 30 and 32 are active high, the output of NOR gate 34 is low or pulled to ground potential. All the inputs for NAND gates 30 and 32 will be active high when the 12 bit binary counter 26 has a value of 1178 decimal. When the output of NOR gate 34 is low the 12 bit counter 26 is reset, effectively dividing the frequency of the 32.768 kHz clock signal 24 by 1178 and resulting in a signal with a frequency of 27.8 Hz. The 27.8 Hz signal is electrically connected to the input of inverter 36 for the purposes of changing the 27.8 Hz signal from active low at the inverter 36 input to active high at the inverter 36 output. The 27.8 Hz signal is the appropriate frequency for the decimal hour timer. By installing jumper J1, the 27.8 Hz signal will be output to the count output 38.
The 27.8 Hz signal is electrically connected to the clock, pin 4, of the divide-by-N circuit 40. The divide-by-N circuit 40 is equivalent to a common digital logic circuit known in the electrical arts as 4522. The divide-by-N circuit is powered by connecting pin 16 to the positive voltage source and is grounded at pin 8. N is defined by binary encoding the value at pins 5, 11, 14 and 2. Connecting pins 11 and 14 to the positive voltage source and pins 5 and 2 to ground, encodes N as 6 for the divide-by-N circuit 40. The 27.8 Hz signal that is received at pin 4 is divided by 6 and outputted at pin 15. The frequency outputted at pin 15 of the divide-by-N circuit 40 is 4.64 Hz. Installing jumper J2 and removing jumper J1, electrically couples the 4.64 Hz signal to the count output 38. By further subdividing the frequency to 4.64 Hz and moving the decimal point in the display, this has the effect of dividing by 60, the difference between hours and minutes, and generating the appropriate frequency for the decimal minute timer mode,
While the above circuit is capable of providing both of the desired frequencies, as will be described in greater detail hereinafter, the hand held timer of the present invention simplifies and reduces the number of parts, and thus the cost and complexity, of the frequency divider circuit to provide a less expensive and simpler hand held decimal hour or minute timer.